diff --git a/src/BusProNet/DataProcessor/BookingDataProcessor.php b/src/BusProNet/DataProcessor/BookingDataProcessor.php
index 104257e..e167d72 100644
--- a/src/BusProNet/DataProcessor/BookingDataProcessor.php
+++ b/src/BusProNet/DataProcessor/BookingDataProcessor.php
@@ -760,6 +760,14 @@ class BookingDataProcessor
             'nationalitaet' => $firstParticipant->nationality ?? '',
         ];
 
+        // Include BPN IDs for linking to existing records (authenticated users)
+        if (null !== $firstParticipant->addressId) {
+            $payload['anmelder']['idadresse'] = $firstParticipant->addressId;
+        }
+        if (null !== $firstParticipant->personId) {
+            $payload['anmelder']['idadresseperson'] = $firstParticipant->personId;
+        }
+
         if (null !== $firstParticipant->dateOfBirth) {
             $payload['anmelder']['geburtsdatum'] = $firstParticipant->dateOfBirth->format('d.m.Y');
         }
@@ -790,6 +798,14 @@ class BookingDataProcessor
                 'nationalitaet' => $participant->nationality ?? '',
             ];
 
+            // Include BPN IDs for linking to existing records (authenticated users)
+            if (null !== $participant->addressId) {
+                $participantData['idadresse'] = $participant->addressId;
+            }
+            if (null !== $participant->personId) {
+                $participantData['idadresseperson'] = $participant->personId;
+            }
+
             if (null !== $participant->dateOfBirth) {
                 $participantData['geburtsdatum'] = $participant->dateOfBirth->format('d.m.Y');
             }
diff --git a/src/Controller/Booking/Create/IndexController.php b/src/Controller/Booking/Create/IndexController.php
index cdbafbe..86fd613 100644
--- a/src/Controller/Booking/Create/IndexController.php
+++ b/src/Controller/Booking/Create/IndexController.php
@@ -32,11 +32,12 @@ class IndexController extends AbstractController
     }
 
     /**
-     * Initializes a fresh booking session and redirects to step 1.
+     * Initializes a fresh booking session and redirects to the login page.
      *
      * This endpoint provides a clean way to start the booking flow with just
-     * dateId and hotelId parameters. It clears any existing booking session
-     * and creates a fresh BookingCreateDto before redirecting to step 1.
+     * dateId and hotelId parameters. It clears any existing booking session,
+     * creates a fresh BookingDto, and redirects to the login page where users
+     * can authenticate (for prepopulation) or continue as guest.
      *
      * Optionally accepts an agency code parameter. If provided and valid, the
      * corresponding agency ID is stored in the booking. If not provided or invalid,
@@ -59,17 +60,17 @@ class IndexController extends AbstractController
             // Create fresh booking session with the provided parameters
             $this->bookingService->startFreshBooking($request, $dateId, $hotelId, $agencyId);
 
-            // Redirect to step 1 of the booking flow
-            return $this->redirectToRoute('app_booking_create_step_1');
-        } catch (TravelNotFoundException $e) {
+            // Redirect to login page (optional authentication before Step 1)
+            return $this->redirectToRoute('app_login');
+        } catch (TravelNotFoundException) {
             throw $this->createNotFoundException(sprintf('Travel not found for date ID %d', $dateId));
-        } catch (HotelNotFoundException $e) {
+        } catch (HotelNotFoundException) {
             throw $this->createNotFoundException(sprintf('Hotel not found for hotel ID %d', $hotelId));
-        } catch (HotelNotInTravelException $e) {
+        } catch (HotelNotInTravelException) {
             throw $this->createNotFoundException(sprintf('Hotel ID %d is not available for travel ID %d', $hotelId, $dateId));
-        } catch (NoRoomsAvailableException $e) {
+        } catch (NoRoomsAvailableException) {
             throw $this->createNotFoundException('No rooms available for this travel.');
-        } catch (BookingNotPossibleException $e) {
+        } catch (BookingNotPossibleException) {
             throw $this->createNotFoundException('Booking is not possible for this travel (Buchungsstop).');
         }
     }
diff --git a/src/Controller/Booking/Create/Step2Controller.php b/src/Controller/Booking/Create/Step2Controller.php
index a72fa01..45dd677 100644
--- a/src/Controller/Booking/Create/Step2Controller.php
+++ b/src/Controller/Booking/Create/Step2Controller.php
@@ -15,6 +15,7 @@ use App\Htmx\HxTrait;
 use App\Service\BookingPriceCalculatorService;
 use App\Service\BookingService;
 use App\Service\ParticipantCardDataService;
+use App\Service\ParticipantPrepopulationService;
 use App\Service\RoomAssignmentService;
 use App\Service\TravelDataService;
 use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
@@ -42,6 +43,7 @@ class Step2Controller extends AbstractController
         private readonly RoomAssignmentService $roomAssignmentService,
         private readonly ParticipantCardDataService $participantCardService,
         private readonly ParticipantFieldOptionsProvider $fieldOptionsProvider,
+        private readonly ParticipantPrepopulationService $prepopulationService,
     ) {
     }
 
@@ -227,10 +229,29 @@ class Step2Controller extends AbstractController
         for ($i = 0; $i < $participantsCount; ++$i) {
             $participant = $participants[$i] ?? new ParticipantDto();
             $participant->index = $i;
+
+            // Prepopulate applicant from authenticated user (index 0 only)
+            if (0 === $i && $this->getUser() && $this->shouldPrepopulate($participant)) {
+                $participant = $this->prepopulationService->prepopulateApplicantFromUser(
+                    $this->getUser(),
+                    $participant
+                );
+            }
+
             $bookingCreateDto->participants[$i] = $participant;
         }
     }
 
+    /**
+     * Determines if a participant should be prepopulated.
+     *
+     * Only prepopulates if the participant is "fresh" (no name set yet).
+     */
+    private function shouldPrepopulate(ParticipantDto $participant): bool
+    {
+        return null === $participant->firstName || '' === $participant->firstName;
+    }
+
     /**
      * Enriches travel data with cached availability information from BusProNet API.
      */
diff --git a/src/Controller/SecurityController.php b/src/Controller/SecurityController.php
index 8733111..72ec7a8 100644
--- a/src/Controller/SecurityController.php
+++ b/src/Controller/SecurityController.php
@@ -2,6 +2,7 @@
 
 namespace App\Controller;
 
+use App\Service\BookingService;
 use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\HttpFoundation\Response;
@@ -13,8 +14,17 @@ class SecurityController extends AbstractController
 {
     #[Route('/', name: 'app_login')]
     #[IsGranted('PUBLIC_ACCESS')]
-    public function login(AuthenticationUtils $authenticationUtils, Request $request): Response
+    public function login(AuthenticationUtils $authenticationUtils, Request $request, BookingService $bookingService): Response
     {
+        // Check if this is a booking flow (BookingDto exists in session)
+        $isBookingFlow = null !== $bookingService->getBookingDto($request, BookingService::BOOKING_CREATE_KEY);
+
+        // If authenticated and in booking flow, proceed to Step 1
+        if (null !== $this->getUser() && true === $isBookingFlow) {
+            return $this->redirectToRoute('app_booking_create_step_1');
+        }
+
+        // If authenticated but not in booking flow, go to personal data
         if (null !== $this->getUser()) {
             return $this->redirectToRoute('app_personal_data');
         }
@@ -31,7 +41,15 @@ class SecurityController extends AbstractController
             $session->set('_oauth2', true);
         }
 
-        return $this->render('security/login.html.twig', [
+        // For booking flow, set target path to Step 1 (after successful auth, redirect there)
+        if (true === $isBookingFlow) {
+            $session->set('_security.main.target_path', $this->generateUrl('app_booking_create_step_1'));
+        }
+
+        // Render booking login template if in booking flow, otherwise standard login
+        $template = true === $isBookingFlow ? 'booking/create/authenticate.html.twig' : 'security/login.html.twig';
+
+        return $this->render($template, [
             'last_username' => $lastUsername,
             'error' => $error,
         ]);
diff --git a/src/Form/BookingParticipantType.php b/src/Form/BookingParticipantType.php
index b86a063..7899805 100644
--- a/src/Form/BookingParticipantType.php
+++ b/src/Form/BookingParticipantType.php
@@ -155,25 +155,35 @@ class BookingParticipantType extends AbstractType
         // Helper to get field state or empty array
         $getFieldState = fn (string $fieldName) => $allFieldStates[$fieldName] ?? [];
 
-        $form
-            ->add('firstName', TextType::class, $this->mergeFieldState([
+        // Add personal data fields with conditional inclusion for authenticated users
+        if ($this->fieldStateProvider->shouldIncludeField('firstName', $bookingDto, $participantIndex)) {
+            $form->add('firstName', TextType::class, $this->mergeFieldState([
                 'label' => 'Vorname',
                 'sanitize_html' => true,
                 'property_path' => 'participant.firstName',
-            ], $getFieldState('firstName')))
-            ->add('lastName', TextType::class, $this->mergeFieldState([
+            ], $getFieldState('firstName')));
+        }
+
+        if ($this->fieldStateProvider->shouldIncludeField('lastName', $bookingDto, $participantIndex)) {
+            $form->add('lastName', TextType::class, $this->mergeFieldState([
                 'label' => 'Nachname',
                 'sanitize_html' => true,
                 'property_path' => 'participant.lastName',
-            ], $getFieldState('lastName')))
-            ->add('dateOfBirth', BirthdayType::class, $this->mergeFieldState([
+            ], $getFieldState('lastName')));
+        }
+
+        if ($this->fieldStateProvider->shouldIncludeField('dateOfBirth', $bookingDto, $participantIndex)) {
+            $form->add('dateOfBirth', BirthdayType::class, $this->mergeFieldState([
                 'label' => 'Geburtsdatum',
                 'widget' => 'text',
                 'input' => 'datetime_immutable',
                 'html5' => false,
                 'property_path' => 'participant.dateOfBirth',
-            ], $getFieldState('dateOfBirth')))
-            ->add('gender', ChoiceType::class, $this->mergeFieldState([
+            ], $getFieldState('dateOfBirth')));
+        }
+
+        if ($this->fieldStateProvider->shouldIncludeField('gender', $bookingDto, $participantIndex)) {
+            $form->add('gender', ChoiceType::class, $this->mergeFieldState([
                 'label' => 'Geschlecht',
                 'required' => false,
                 'placeholder' => 'keine Angabe',
@@ -183,28 +193,41 @@ class BookingParticipantType extends AbstractType
                     'divers' => 'D',
                 ],
                 'property_path' => 'participant.gender',
-            ], $getFieldState('gender')))
-            ->add('nationality', CountryType::class, $this->mergeFieldState([
+            ], $getFieldState('gender')));
+        }
+
+        if ($this->fieldStateProvider->shouldIncludeField('nationality', $bookingDto, $participantIndex)) {
+            $form->add('nationality', CountryType::class, $this->mergeFieldState([
                 'label' => 'Nationalität',
                 'property' => 'nationality',
                 'preferred_choices' => ['D', 'A', 'CH'],
                 'property_path' => 'participant.nationality',
-            ], $getFieldState('nationality')))
-            ->add('email', EmailType::class, $this->mergeFieldState([
+            ], $getFieldState('nationality')));
+        }
+
+        if ($this->fieldStateProvider->shouldIncludeField('email', $bookingDto, $participantIndex)) {
+            $form->add('email', EmailType::class, $this->mergeFieldState([
                 'label' => 'E-Mail',
                 'property_path' => 'participant.email',
-            ], $getFieldState('email')))
-            ->add('mobile', TextType::class, $this->mergeFieldState([
+            ], $getFieldState('email')));
+        }
+
+        if ($this->fieldStateProvider->shouldIncludeField('mobile', $bookingDto, $participantIndex)) {
+            $form->add('mobile', TextType::class, $this->mergeFieldState([
                 'label' => 'Telefon (mobil)',
                 'required' => false,
                 'sanitize_html' => true,
                 'property_path' => 'participant.mobile',
-            ], $getFieldState('mobile')))
-            ->add('address', AddressType::class, $this->mergeFieldState([
+            ], $getFieldState('mobile')));
+        }
+
+        if ($this->fieldStateProvider->shouldIncludeField('address', $bookingDto, $participantIndex)) {
+            $form->add('address', AddressType::class, $this->mergeFieldState([
                 'label' => 'Adresse',
                 'required' => false,
                 'property_path' => 'participant.address',
             ], $getFieldState('address')));
+        }
 
         // Add body dimensions with state handling - use shouldIncludeField method
         if ($this->fieldStateProvider->shouldIncludeField('bodyDimensions', $bookingDto, $participantIndex)) {
diff --git a/src/Form/Model/ParticipantDto.php b/src/Form/Model/ParticipantDto.php
index 753d149..146c205 100644
--- a/src/Form/Model/ParticipantDto.php
+++ b/src/Form/Model/ParticipantDto.php
@@ -128,6 +128,7 @@ class ParticipantDto
         $instance->mutable = $personalData->mutable;
         $instance->firstName = $personalData->firstName;
         $instance->lastName = $personalData->name;
+        $instance->title = $personalData->title;
         $instance->gender = $personalData->gender;
         $instance->nationality = $personalData->nationality;
         $instance->email = $personalData->communication?->email;
diff --git a/src/Form/Service/Condition/AuthenticatedUserPersonalDataCondition.php b/src/Form/Service/Condition/AuthenticatedUserPersonalDataCondition.php
new file mode 100644
index 0000000..2dfd373
--- /dev/null
+++ b/src/Form/Service/Condition/AuthenticatedUserPersonalDataCondition.php
@@ -0,0 +1,76 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Form\Service\Condition;
+
+use App\Form\Model\BookingDto;
+use App\Form\Service\Contract\FieldConditionInterface;
+
+/**
+ * Condition that determines if personal data fields should be hidden for authenticated users.
+ *
+ * When a participant is linked to an existing BPN account (has addressId and personId),
+ * their personal data should not be editable during the booking process. Changes to
+ * master personal data should only happen through the dedicated personal data management
+ * interface to prevent:
+ * - Creating duplicate customer records in BPN
+ * - Disconnecting bookings from the user's account
+ * - Data inconsistencies between booking and account data
+ *
+ * When this condition is satisfied (returns true), the template should:
+ * - Hide the form fields for personal data
+ * - Display the values as static, read-only text
+ *
+ * This follows the same pattern as bulk insurance booking.
+ */
+class AuthenticatedUserPersonalDataCondition implements FieldConditionInterface
+{
+    /**
+     * Evaluates if personal data fields should be hidden (not editable).
+     *
+     * Returns true when the participant has both addressId and personId set,
+     * indicating they are linked to an existing BPN account. When true,
+     * personal data fields should be hidden and displayed as static text.
+     *
+     * @param BookingDto           $bookingDto       The current booking data
+     * @param int                  $participantIndex The index of the participant being evaluated
+     * @param array<string, mixed> $formData         Current form data (unused)
+     *
+     * @return bool True if fields should be hidden (participant linked to BPN account)
+     */
+    public function evaluate(BookingDto $bookingDto, int $participantIndex, array $formData): bool
+    {
+        $participant = $bookingDto->getParticipant($participantIndex);
+        if (null === $participant) {
+            return false;
+        }
+
+        // Hide personal data fields if participant has BPN account IDs
+        // (indicates prepopulation from authenticated user)
+        return null !== $participant->addressId && null !== $participant->personId;
+    }
+
+    /**
+     * Returns field names that this condition depends on.
+     *
+     * This condition is based on addressId/personId which are set during prepopulation
+     * and don't change during the form interaction, so no field dependencies.
+     *
+     * @return string[] Empty array - no field dependencies
+     */
+    public function getDependentFields(): array
+    {
+        return [];
+    }
+
+    /**
+     * Returns a human-readable description of this condition.
+     *
+     * @return string Description of the authenticated user personal data protection logic
+     */
+    public function getDescription(): string
+    {
+        return 'Personal data is not editable when participant is linked to BPN account (prevents duplicate records)';
+    }
+}
diff --git a/src/Form/Service/CreateFieldStateProvider.php b/src/Form/Service/CreateFieldStateProvider.php
index 07348cc..3a5cf8f 100644
--- a/src/Form/Service/CreateFieldStateProvider.php
+++ b/src/Form/Service/CreateFieldStateProvider.php
@@ -7,6 +7,7 @@ namespace App\Form\Service;
 use App\BusProNet\Utility\DirectionMapper;
 use App\Form\Service\Abstract\AbstractFieldStateProvider;
 use App\Form\Service\Condition\ApplicantCondition;
+use App\Form\Service\Condition\AuthenticatedUserPersonalDataCondition;
 use App\Form\Service\Condition\BookingEligibilityCondition;
 use App\Form\Service\Condition\BulkInsuranceBookingCondition;
 use App\Form\Service\Condition\CompositeCondition;
@@ -73,6 +74,64 @@ class CreateFieldStateProvider extends AbstractFieldStateProvider
         $rentalCondition = new RentalSelectionCondition();
         $skiPassCondition = new SkiPassSelectionCondition();
 
+        // Authenticated user personal data protection
+        // Hide personal data fields for participants linked to BPN accounts (prevents duplicate records)
+        $authenticatedUserCondition = new AuthenticatedUserPersonalDataCondition();
+
+        $this->fieldStateConditions['firstName'] = [
+            'hidden' => $authenticatedUserCondition,
+        ];
+
+        $this->fieldStateConditions['lastName'] = [
+            'hidden' => $authenticatedUserCondition,
+        ];
+
+        $this->fieldStateConditions['gender'] = [
+            'hidden' => $authenticatedUserCondition,
+        ];
+
+        $this->fieldStateConditions['nationality'] = [
+            'hidden' => $authenticatedUserCondition,
+        ];
+
+        $this->fieldStateConditions['dateOfBirth'] = [
+            'hidden' => $authenticatedUserCondition,
+        ];
+
+        $this->fieldStateConditions['email'] = [
+            'hidden' => $authenticatedUserCondition,
+        ];
+
+        // Mobile field: hidden for authenticated users, required for guest applicants
+        $this->fieldStateConditions['mobile'] = [
+            'hidden' => $authenticatedUserCondition,
+            'required' => new ApplicantCondition(),
+        ];
+
+        // Address subfields - must be hidden to prevent creating duplicate BPN records
+        $this->fieldStateConditions['address.street'] = [
+            'hidden' => $authenticatedUserCondition,
+        ];
+
+        $this->fieldStateConditions['address.postCode'] = [
+            'hidden' => $authenticatedUserCondition,
+        ];
+
+        $this->fieldStateConditions['address.city'] = [
+            'hidden' => $authenticatedUserCondition,
+        ];
+
+        $this->fieldStateConditions['address.country'] = [
+            'hidden' => $authenticatedUserCondition,
+        ];
+
+        $this->fieldStateConditions['address.district'] = [
+            'hidden' => $authenticatedUserCondition,
+        ];
+
+        // Note: Body dimensions (height, weight, shoeSize) are NOT hidden for authenticated users
+        // These are preferences/measurements that can be updated without creating duplicate records
+
         // Hide body dimensions section unless rental services are selected
         $this->fieldStateConditions['bodyDimensions'] = [
             'hidden' => CompositeCondition::not($rentalCondition),
@@ -195,11 +254,6 @@ class CreateFieldStateProvider extends AbstractFieldStateProvider
             'hidden' => FieldValueCondition::equals('parking', false),
         ];
 
-        // Make mobile field required for applicant (participant index 0)
-        $this->fieldStateConditions['mobile'] = [
-            'required' => new ApplicantCondition(),
-        ];
-
         // Make address field required for applicant (participant index 0)
         $this->fieldStateConditions['address'] = [
             'required' => new ApplicantCondition(),
diff --git a/src/Service/ParticipantPrepopulationService.php b/src/Service/ParticipantPrepopulationService.php
new file mode 100644
index 0000000..3ea25a1
--- /dev/null
+++ b/src/Service/ParticipantPrepopulationService.php
@@ -0,0 +1,101 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Service;
+
+use App\BusProNet\ApiClient;
+use App\BusProNet\Model\Notification;
+use App\Entity\User;
+use App\Form\Model\ParticipantDto;
+use App\Security\Crypt;
+use Psr\Log\LoggerInterface;
+
+/**
+ * Service for prepopulating participant data from authenticated user's personal data.
+ *
+ * Fetches personal data from BPN API and maps it to a ParticipantDto to streamline
+ * the booking process for authenticated users. All errors are handled gracefully
+ * to ensure the booking flow is never interrupted.
+ */
+class ParticipantPrepopulationService
+{
+    public function __construct(
+        private readonly ApiClient $apiClient,
+        private readonly Crypt $crypt,
+        private readonly LoggerInterface $logger,
+    ) {
+    }
+
+    /**
+     * Prepopulates applicant data from authenticated user's personal data.
+     *
+     * Fetches PersonalData from BPN API using the user's credentials and maps
+     * the data to the provided ParticipantDto. If the API call fails or returns
+     * incomplete data, the method logs the error and returns the unpopulated
+     * participant without throwing exceptions.
+     *
+     * @param User           $user      The authenticated user
+     * @param ParticipantDto $applicant The applicant DTO to prepopulate
+     *
+     * @return ParticipantDto The prepopulated participant (or unchanged if API fails)
+     */
+    public function prepopulateApplicantFromUser(User $user, ParticipantDto $applicant): ParticipantDto
+    {
+        try {
+            // Decrypt user password for API authentication
+            $password = $this->crypt->decrypt($user->getPassword());
+            $email = $user->getEmail();
+
+            // Fetch personal data from API
+            $result = $this->apiClient->getPersonalData($email, $password);
+
+            // Handle API error response
+            if ($result instanceof Notification) {
+                $this->logger->warning('Failed to fetch personal data for prepopulation', [
+                    'email' => $email,
+                    'code' => $result->code,
+                    'message' => $result->message,
+                ]);
+
+                return $applicant;
+            }
+
+            // Create a temporary participant from personal data
+            $prepopulated = ParticipantDto::fromPersonalData($result);
+
+            // Copy personal data fields to the existing applicant
+            // Preserve booking-specific fields (roomId, services, etc.)
+            $applicant->addressId = $prepopulated->addressId;
+            $applicant->personId = $prepopulated->personId;
+            $applicant->firstName = $prepopulated->firstName;
+            $applicant->lastName = $prepopulated->lastName;
+            $applicant->title = $prepopulated->title;
+            $applicant->gender = $prepopulated->gender;
+            $applicant->nationality = $prepopulated->nationality;
+            $applicant->dateOfBirth = $prepopulated->dateOfBirth;
+            $applicant->email = $prepopulated->email;
+            $applicant->mobile = $prepopulated->mobile;
+            $applicant->address = $prepopulated->address;
+            $applicant->height = $prepopulated->height;
+            $applicant->weight = $prepopulated->weight;
+            $applicant->shoeSize = $prepopulated->shoeSize;
+            $applicant->remarksRoom = $prepopulated->remarksRoom;
+            $applicant->licensePlate = $prepopulated->licensePlate;
+
+            $this->logger->info('Prepopulated applicant data from user profile', [
+                'email' => $email,
+            ]);
+
+            return $applicant;
+        } catch (\Exception $e) {
+            // Catch any unexpected exceptions (decryption failure, API errors, etc.)
+            $this->logger->error('Exception during applicant prepopulation', [
+                'error' => $e->getMessage(),
+                'email' => $user->getEmail(),
+            ]);
+
+            return $applicant;
+        }
+    }
+}
diff --git a/templates/booking/_participant_form.html.twig b/templates/booking/_participant_form.html.twig
index 2930ba5..f3a9da5 100644
--- a/templates/booking/_participant_form.html.twig
+++ b/templates/booking/_participant_form.html.twig
@@ -46,24 +46,88 @@
         <div id="participant-form" class="space-y-4">
             {# Personal data section #}
             <div class="grid grid-cols-2 gap-4">
-                {{ form_row(form.firstName) }}
-                {{ form_row(form.lastName) }}
-                {{ form_row(form.dateOfBirth, {
-                    'attr': {
-                        'hx-trigger': 'change',
-                        'hx-post': path(refreshRouteName, refreshRouteParams|default({index: participantIndex})),
-                        'hx-target': '#main-content',
-                        'hx-swap': 'innerHTML'
-                    }
-                }) }}
-                {{ form_row(form.gender) }}
-                {{ form_row(form.nationality) }}
+                {% if form.firstName is defined %}
+                    {{ form_row(form.firstName) }}
+                {% else %}
+                    <div>
+                        <label class="font-semibold mb-1 block">Vorname</label>
+                        <div class="text-sm text-gray-600">{{ form.vars.data.participant.firstName }}</div>
+                    </div>
+                {% endif %}
+
+                {% if form.lastName is defined %}
+                    {{ form_row(form.lastName) }}
+                {% else %}
+                    <div>
+                        <label class="font-semibold mb-1 block">Nachname</label>
+                        <div class="text-sm text-gray-600">{{ form.vars.data.participant.lastName }}</div>
+                    </div>
+                {% endif %}
+
+                {% if form.dateOfBirth is defined %}
+                    {{ form_row(form.dateOfBirth, {
+                        'attr': {
+                            'hx-trigger': 'change',
+                            'hx-post': path(refreshRouteName, refreshRouteParams|default({index: participantIndex})),
+                            'hx-target': '#main-content',
+                            'hx-swap': 'innerHTML'
+                        }
+                    }) }}
+                {% else %}
+                    <div>
+                        <label class="font-semibold mb-1 block">Geburtsdatum</label>
+                        <div class="text-sm text-gray-600">{{ form.vars.data.participant.dateOfBirth ? form.vars.data.participant.dateOfBirth|date('d.m.Y') : '-' }}</div>
+                    </div>
+                {% endif %}
+
+                {% if form.gender is defined %}
+                    {{ form_row(form.gender) }}
+                {% else %}
+                    <div>
+                        <label class="font-semibold mb-1 block">Geschlecht</label>
+                        <div class="text-sm text-gray-600">
+                            {% if form.vars.data.participant.gender == 'M' %}
+                                männlich
+                            {% elseif form.vars.data.participant.gender == 'W' %}
+                                weiblich
+                            {% elseif form.vars.data.participant.gender == 'D' %}
+                                divers
+                            {% else %}
+                                -
+                            {% endif %}
+                        </div>
+                    </div>
+                {% endif %}
+
+                {% if form.nationality is defined %}
+                    {{ form_row(form.nationality) }}
+                {% else %}
+                    <div>
+                        <label class="font-semibold mb-1 block">Nationalität</label>
+                        <div class="text-sm text-gray-600">{{ form.vars.data.participant.nationality ?: '-' }}</div>
+                    </div>
+                {% endif %}
             </div>
 
             {# Contact information #}
             <div class="grid grid-cols-2 gap-4">
-                {{ form_row(form.email) }}
-                {{ form_row(form.mobile) }}
+                {% if form.email is defined %}
+                    {{ form_row(form.email) }}
+                {% else %}
+                    <div>
+                        <label class="font-semibold mb-1 block">E-Mail</label>
+                        <div class="text-sm text-gray-600">{{ form.vars.data.participant.email }}</div>
+                    </div>
+                {% endif %}
+
+                {% if form.mobile is defined %}
+                    {{ form_row(form.mobile) }}
+                {% else %}
+                    <div>
+                        <label class="font-semibold mb-1 block">Telefon (mobil)</label>
+                        <div class="text-sm text-gray-600">{{ form.vars.data.participant.mobile ?: '-' }}</div>
+                    </div>
+                {% endif %}
             </div>
 
             {# Address #}
@@ -74,6 +138,21 @@
                     {{ form_row(form.address.city) }}
                     {{ form_row(form.address.country) }}
                 </div>
+            {% else %}
+                <div>
+                    <label class="font-semibold mb-1 block">Adresse</label>
+                    {% if form.vars.data.participant.address %}
+                        <div class="text-sm text-gray-600">
+                            {% if form.vars.data.participant.address.street %}{{ form.vars.data.participant.address.street }}<br>{% endif %}
+                            {% if form.vars.data.participant.address.postCode or form.vars.data.participant.address.city %}
+                                {{ form.vars.data.participant.address.postCode }} {{ form.vars.data.participant.address.city }}<br>
+                            {% endif %}
+                            {% if form.vars.data.participant.address.country %}{{ form.vars.data.participant.address.country }}{% endif %}
+                        </div>
+                    {% else %}
+                        <div class="text-sm text-gray-600">-</div>
+                    {% endif %}
+                </div>
             {% endif %}
 
             {# Room assignment #}
diff --git a/templates/booking/create/authenticate.html.twig b/templates/booking/create/authenticate.html.twig
new file mode 100644
index 0000000..ac615f3
--- /dev/null
+++ b/templates/booking/create/authenticate.html.twig
@@ -0,0 +1,103 @@
+{% extends 'layout.html.twig' %}
+
+{% block content %}
+    {% include '_partials/_flashes.html.twig' %}
+
+    <h1 class="mb-4">
+        Neue Buchung
+    </h1>
+
+    <div class="bg-blue-50 border border-blue-200 rounded-lg p-6 mb-6">
+        <h2 class="text-blue-900 font-semibold text-lg mb-3">
+            Optional: Anmelden für schnelleres Buchen
+        </h2>
+        <p class="text-blue-800 mb-2">
+            Melde dich an, um deine persönlichen Daten automatisch in die Buchung zu übernehmen.
+            Dies ist <strong>vollständig optional</strong> – du kannst auch ohne Anmeldung als Gast fortfahren.
+        </p>
+    </div>
+
+    <div class="grid grid-cols-1 md:grid-cols-2 gap-8">
+        {# Login Form #}
+        <div>
+            <h3 class="mb-4 font-semibold text-lg">
+                Mit bestehendem Account anmelden
+            </h3>
+
+            {% if error %}
+                {% include '_partials/_alert.html.twig' with { 'level': 'error', messages: [ error.messageKey|trans(error.messageData, 'security') ] } %}
+            {% endif %}
+
+            <form action="{{ path('app_login') }}" method="post" {{ stimulus_action('loading', 'toggle') }}>
+                <div class="mb-4">
+                    <label for="username" class="mb-1 font-semibold">
+                        E-Mail:
+                    </label>
+                    <input type="email"
+                           id="username"
+                           name="_username"
+                           value="{{ last_username }}"
+                           class="form-field"
+                           required
+                           autocomplete="username">
+                </div>
+
+                <div class="mb-4">
+                    <label for="password" class="mb-1 font-semibold">
+                        Passwort:
+                    </label>
+                    <input type="password"
+                           id="password"
+                           name="_password"
+                           class="form-field"
+                           required
+                           autocomplete="current-password">
+                </div>
+
+                <div class="mb-4">
+                    <label class="flex items-center">
+                        <input type="checkbox" name="_remember_me" class="mr-2">
+                        <span class="text-sm">Angemeldet bleiben</span>
+                    </label>
+                </div>
+
+                <div class="flex flex-col space-y-2">
+                    <button type="submit" class="button bg-button">
+                        Anmelden und fortfahren
+                    </button>
+                    <a href="{{ path('app_reset_password') }}"
+                       class="text-sm text-center text-blue-600 hover:underline">
+                        Passwort vergessen?
+                    </a>
+                </div>
+
+                <input type="hidden" name="_csrf_token" value="{{ csrf_token('authenticate') }}">
+            </form>
+        </div>
+
+        {# Continue as Guest #}
+        <div>
+            <h3 class="mb-4 font-semibold text-lg">
+                Als Gast fortfahren
+            </h3>
+
+            <p class="mb-4 text-gray-700">
+                Du kannst auch ohne Anmeldung buchen. Deine persönlichen Daten gibst du dann im nächsten Schritt ein.
+            </p>
+
+            <a href="{{ path('app_booking_create_step_1') }}" class="button bg-button bg-button--secondary w-full block text-center">
+                Als Gast fortfahren
+            </a>
+
+            <div class="mt-6 p-4 bg-gray-50 border border-gray-200 rounded">
+                <h4 class="font-semibold mb-2 text-sm">
+                    Noch kein Account?
+                </h4>
+                <p class="text-sm text-gray-700">
+                    Nach Abschluss deiner Buchung wird automatisch ein Account für dich erstellt.
+                    Du erhältst dann Zugangsdaten per E-Mail und kannst deine Buchungen jederzeit verwalten.
+                </p>
+            </div>
+        </div>
+    </div>
+{% endblock %}
\ No newline at end of file
diff --git a/templates/booking/create/success.html.twig b/templates/booking/create/success.html.twig
index 8721bfe..ce7527c 100644
--- a/templates/booking/create/success.html.twig
+++ b/templates/booking/create/success.html.twig
@@ -16,8 +16,24 @@
             </p>
         </div>
 
-        <a href="https://www.ep-reisen.de" class="button bg-button bg-button--primary">
-            Zurück zur Startseite
-        </a>
+        {% if app.user %}
+            {# Authenticated user - show account-related actions #}
+            <div class="space-y-4">
+                <a href="{{ path('app_personal_data') }}" class="button bg-button bg-button--primary inline-block">
+                    Zu meinen persönlichen Daten
+                </a>
+                <a href="{{ path('app_bookings') }}" class="button bg-button bg-button--secondary inline-block ml-2">
+                    Meine Buchungen anzeigen
+                </a>
+                <a href="{{ path('app_logout') }}" class="button bg-button bg-button--outline inline-block ml-2">
+                    Abmelden
+                </a>
+            </div>
+        {% else %}
+            {# Guest user - show simple homepage link #}
+            <a href="https://www.ep-reisen.de" class="button bg-button bg-button--primary">
+                Zurück zur Startseite
+            </a>
+        {% endif %}
     </div>
 {% endblock %}
diff --git a/tests/Service/ParticipantPrepopulationServiceTest.php b/tests/Service/ParticipantPrepopulationServiceTest.php
new file mode 100644
index 0000000..2b23131
--- /dev/null
+++ b/tests/Service/ParticipantPrepopulationServiceTest.php
@@ -0,0 +1,307 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests\Service;
+
+use App\BusProNet\ApiClient;
+use App\BusProNet\Model\Address;
+use App\BusProNet\Model\Communication;
+use App\BusProNet\Model\Notification;
+use App\BusProNet\Model\PersonalData;
+use App\Entity\User;
+use App\Form\Model\ParticipantDto;
+use App\Security\Crypt;
+use App\Service\ParticipantPrepopulationService;
+use PHPUnit\Framework\TestCase;
+use Psr\Log\LoggerInterface;
+
+class ParticipantPrepopulationServiceTest extends TestCase
+{
+    private ApiClient $apiClient;
+    private Crypt $crypt;
+    private LoggerInterface $logger;
+    private ParticipantPrepopulationService $service;
+
+    protected function setUp(): void
+    {
+        $this->apiClient = $this->createMock(ApiClient::class);
+        $this->crypt = $this->createMock(Crypt::class);
+        $this->logger = $this->createMock(LoggerInterface::class);
+
+        $this->service = new ParticipantPrepopulationService(
+            $this->apiClient,
+            $this->crypt,
+            $this->logger
+        );
+    }
+
+    public function testPrepopulateApplicantWithCompletePersonalData(): void
+    {
+        $user = $this->createUser('test@example.com', 'encrypted_password');
+        $applicant = new ParticipantDto();
+        $applicant->index = 0;
+
+        $personalData = $this->createCompletePersonalData();
+
+        $this->crypt->expects($this->once())
+            ->method('decrypt')
+            ->with('encrypted_password')
+            ->willReturn('decrypted_password');
+
+        $this->apiClient->expects($this->once())
+            ->method('getPersonalData')
+            ->with('test@example.com', 'decrypted_password')
+            ->willReturn($personalData);
+
+        $this->logger->expects($this->once())
+            ->method('info')
+            ->with('Prepopulated applicant data from user profile', ['email' => 'test@example.com']);
+
+        $result = $this->service->prepopulateApplicantFromUser($user, $applicant);
+
+        // BPN API IDs for linking to existing records
+        $this->assertSame(12345, $result->addressId);
+        $this->assertSame(67890, $result->personId);
+
+        $this->assertSame('John', $result->firstName);
+        $this->assertSame('Doe', $result->lastName);
+        $this->assertSame('Dr.', $result->title);
+        $this->assertSame('M', $result->gender);
+        $this->assertSame('DE', $result->nationality);
+        $this->assertSame('test@example.com', $result->email);
+        $this->assertSame('+49123456789', $result->mobile);
+        $this->assertSame('180', $result->height);
+        $this->assertSame('75', $result->weight);
+        $this->assertSame('42', $result->shoeSize);
+        $this->assertSame('No smoking room please', $result->remarksRoom);
+        $this->assertSame('AB-CD-1234', $result->licensePlate);
+
+        $this->assertNotNull($result->dateOfBirth);
+        $this->assertSame('1990-05-15', $result->dateOfBirth->format('Y-m-d'));
+
+        $this->assertNotNull($result->address);
+        $this->assertSame('Main Street 123', $result->address->street);
+        $this->assertSame('12345', $result->address->postCode);
+        $this->assertSame('Berlin', $result->address->city);
+        $this->assertSame('DE', $result->address->country);
+        $this->assertSame('Mitte', $result->address->district);
+    }
+
+    public function testPrepopulateApplicantWithPartialPersonalData(): void
+    {
+        $user = $this->createUser('test@example.com', 'encrypted_password');
+        $applicant = new ParticipantDto();
+        $applicant->index = 0;
+
+        $personalData = $this->createPartialPersonalData();
+
+        $this->crypt->expects($this->once())
+            ->method('decrypt')
+            ->willReturn('decrypted_password');
+
+        $this->apiClient->expects($this->once())
+            ->method('getPersonalData')
+            ->willReturn($personalData);
+
+        $this->logger->expects($this->once())
+            ->method('info');
+
+        $result = $this->service->prepopulateApplicantFromUser($user, $applicant);
+
+        // Required fields should be populated
+        $this->assertSame('Jane', $result->firstName);
+        $this->assertSame('Smith', $result->lastName);
+        $this->assertSame('jane@example.com', $result->email);
+
+        // Optional fields should be null
+        $this->assertNull($result->title);
+        $this->assertNull($result->gender);
+        $this->assertNull($result->nationality);
+        $this->assertNull($result->mobile);
+        $this->assertNull($result->height);
+        $this->assertNull($result->weight);
+        $this->assertNull($result->shoeSize);
+        $this->assertNull($result->remarksRoom);
+        $this->assertNull($result->licensePlate);
+    }
+
+    public function testPrepopulateApplicantWithApiNotificationError(): void
+    {
+        $user = $this->createUser('test@example.com', 'encrypted_password');
+        $applicant = new ParticipantDto();
+        $applicant->index = 0;
+
+        $notification = new Notification(401, 'Authentication failed');
+
+        $this->crypt->expects($this->once())
+            ->method('decrypt')
+            ->willReturn('decrypted_password');
+
+        $this->apiClient->expects($this->once())
+            ->method('getPersonalData')
+            ->willReturn($notification);
+
+        $this->logger->expects($this->once())
+            ->method('warning')
+            ->with('Failed to fetch personal data for prepopulation', [
+                'email' => 'test@example.com',
+                'code' => 401,
+                'message' => 'Authentication failed',
+            ]);
+
+        $this->logger->expects($this->never())
+            ->method('info');
+
+        $result = $this->service->prepopulateApplicantFromUser($user, $applicant);
+
+        // Should return unchanged applicant
+        $this->assertNull($result->firstName);
+        $this->assertNull($result->lastName);
+        $this->assertNull($result->email);
+    }
+
+    public function testPrepopulateApplicantWithDecryptionException(): void
+    {
+        $user = $this->createUser('test@example.com', 'encrypted_password');
+        $applicant = new ParticipantDto();
+        $applicant->index = 0;
+
+        $this->crypt->expects($this->once())
+            ->method('decrypt')
+            ->willThrowException(new \RuntimeException('Decryption failed'));
+
+        $this->apiClient->expects($this->never())
+            ->method('getPersonalData');
+
+        $this->logger->expects($this->once())
+            ->method('error')
+            ->with('Exception during applicant prepopulation', [
+                'error' => 'Decryption failed',
+                'email' => 'test@example.com',
+            ]);
+
+        $result = $this->service->prepopulateApplicantFromUser($user, $applicant);
+
+        // Should return unchanged applicant
+        $this->assertNull($result->firstName);
+        $this->assertNull($result->lastName);
+        $this->assertNull($result->email);
+    }
+
+    public function testPrepopulateApplicantWithApiException(): void
+    {
+        $user = $this->createUser('test@example.com', 'encrypted_password');
+        $applicant = new ParticipantDto();
+        $applicant->index = 0;
+
+        $this->crypt->expects($this->once())
+            ->method('decrypt')
+            ->willReturn('decrypted_password');
+
+        $this->apiClient->expects($this->once())
+            ->method('getPersonalData')
+            ->willThrowException(new \RuntimeException('API connection failed'));
+
+        $this->logger->expects($this->once())
+            ->method('error')
+            ->with('Exception during applicant prepopulation', [
+                'error' => 'API connection failed',
+                'email' => 'test@example.com',
+            ]);
+
+        $result = $this->service->prepopulateApplicantFromUser($user, $applicant);
+
+        // Should return unchanged applicant
+        $this->assertNull($result->firstName);
+        $this->assertNull($result->lastName);
+        $this->assertNull($result->email);
+    }
+
+    public function testPrepopulatePreservesBookingSpecificFields(): void
+    {
+        $user = $this->createUser('test@example.com', 'encrypted_password');
+        $applicant = new ParticipantDto();
+        $applicant->index = 0;
+        $applicant->assignedRoomId = 42;
+        $applicant->bulkInsuranceBooking = true;
+
+        $personalData = $this->createCompletePersonalData();
+
+        $this->crypt->expects($this->once())
+            ->method('decrypt')
+            ->willReturn('decrypted_password');
+
+        $this->apiClient->expects($this->once())
+            ->method('getPersonalData')
+            ->willReturn($personalData);
+
+        $result = $this->service->prepopulateApplicantFromUser($user, $applicant);
+
+        // Personal data should be updated
+        $this->assertSame('John', $result->firstName);
+        $this->assertSame('Doe', $result->lastName);
+
+        // Booking-specific fields should be preserved
+        $this->assertSame(42, $result->assignedRoomId);
+        $this->assertTrue($result->bulkInsuranceBooking);
+    }
+
+    private function createUser(string $email, string $encryptedPassword): User
+    {
+        $user = new User($email);
+        $user->setPassword($encryptedPassword);
+
+        return $user;
+    }
+
+    private function createCompletePersonalData(): PersonalData
+    {
+        $personalData = new PersonalData();
+        $personalData->addressId = 12345;
+        $personalData->personId = 67890;
+        $personalData->firstName = 'John';
+        $personalData->name = 'Doe';
+        $personalData->title = 'Dr.';
+        $personalData->gender = 'M';
+        $personalData->nationality = 'DE';
+        $personalData->dateOfBirth = new \DateTimeImmutable('1990-05-15');
+        $personalData->height = '180';
+        $personalData->weight = '75';
+        $personalData->shoeSize = '42';
+        $personalData->remarksRoom = 'No smoking room please';
+        $personalData->licensePlate = 'AB-CD-1234';
+
+        $personalData->communication = new Communication();
+        $personalData->communication->email = 'test@example.com';
+        $personalData->communication->mobile = '+49123456789';
+
+        $personalData->address = new Address();
+        $personalData->address->street = 'Main Street 123';
+        $personalData->address->postCode = '12345';
+        $personalData->address->city = 'Berlin';
+        $personalData->address->country = 'DE';
+        $personalData->address->district = 'Mitte';
+
+        return $personalData;
+    }
+
+    private function createPartialPersonalData(): PersonalData
+    {
+        $personalData = new PersonalData();
+        $personalData->firstName = 'Jane';
+        $personalData->name = 'Smith';
+        $personalData->dateOfBirth = new \DateTimeImmutable('1995-03-20');
+
+        $personalData->communication = new Communication();
+        $personalData->communication->email = 'jane@example.com';
+
+        $personalData->address = new Address();
+        $personalData->address->street = 'Second Street 45';
+        $personalData->address->postCode = '54321';
+        $personalData->address->city = 'Munich';
+        $personalData->address->country = 'DE';
+
+        return $personalData;
+    }
+}